Is "Link 1 2" in the descriptors obsolete?
It looks like we're up to link protocol 4 in practice, but the descriptors still write this static string:
"protocols Link 1 2 Circuit 1\n"
dir-spec.txt tells us
Both lists are space-separated sequences of numbers, to indicate which protocols the server supports. As of 30 Mar 2008, specified protocols are "Link 1 2 Circuit 1". See section 4.1 of tor-spec.txt for more information about link protocol versions.
but Section 4.1 of tor-spec.txt indeed admits to link protocols 3 and 4.
It looks like nothing in routerparse.c or anywhere else looks at the 'protocols' line of the descriptor. Heck, normal clients don't even get the descriptor anymore.
I assume the last Tor version to not understand link protocol 2 is way obsolete (Tor 0.2.0.x era I think).
And if clients never see the descriptors, it's hard to imagine how we'll be able to tell them a different Circuit protocol either.
Should we dump this line? Have we accidentally lost anything here?